Congratulations to S. Prabhakaran for publishing a recent paper entitled “Laser shock peening without coating induced residual stress distribution, wettability characteristics and enhanced pitting corrosion resistance of austenitic stainless steel”.
This paper is focused on low energy laser shock peening without coating (LSPwC) to modify the properties of AISI 304 austenitic stainless steel.
The results were very interesting and will find many applications where such improvements in the material property could render additional benefits to the various industrial problems associated with stain-less steel, since LSPwC could conveniently induced high magnitude of compressive residual stresses, controlled roughness, increase wettability characteristics; reduce pitting corrosion with phase transformation, microstructural refinement as well as enhance hardness.
Over time, S. Prabhakaran and Prof. Kalainathan (from Vellore Institution of Technology (VIT University), Vellore, Tamil Nadu, India) have been collaborators with Dr Shukla and the work is currently on going to see the wider effects of low energy, low cost LSPwC research suitable to specific applications of austenitic stainless steel as well as other materials. More updates to come on this, as the work is on-going. Please see the highlights, abstract, citation and the link to the paper below:
75% laser pulse overlapping was induced large and higher magnitude of compressive residual stress during LSPwC.
The excess surface roughness induction was controlled via optimized laser pulse overlapping.
Hydrophilic to Hydrophobic nature increases the wettability characteristics.
Martensite phase transformation trend and microstructural grain refinement features are observed with 28% hardness improvement.
Pitting corrosion resistance and stable passivation layer improved the corrosion properties of austenitic stainless steel.
Low energy laser shock peening without coating (LSPwC) was conducted on AISI 304 austenitic stainless steel specimens with varying pulse densities or overlapping. Highest magnitude of compressive residual stress (CRS) was achieved for an optimized pulse density of 2500 pulses/cm2 (75% overlapping). The 2-D and 3-D topographical analysis were indicative of the fact that controlled roughening of the surface was achieved after the LSPwC process. After the LSPwC process, the hydrophilic unpeened surface was converted into the hydrophobic surface, thus decreasing the wettability characteristics of the surface. The X-ray diffraction (XRD) results reveal that there is a beginning of the martensite transformation and the rise in the intensity value of the peaks after LSPwC indicates the presence of compressive residual stresses induced in the specimen. The optical microscope and high-resolution transmission electron microscope results provided evidence of grain refinement and deformation induced refinement features such as multidirectional mechanical twinning, dislocations lines, micro shear cells and stacking faults in the near and sub-surface areas. The average hardness value of the LSPwC specimens was found to be increased by 28% more than the untreated specimen. The potentiodynamic polarization revealed that there was a considerable amount of increase in the pitting corrosion resistance after the LSPwC process, thus, supporting to extend the fatigue life of the specimen. The electrochemical impedance spectroscopic (EIS) analysis depicts that the LSPwC process supports the formation of the strong passivation layer in 3.5% NaCl solution.
S. Prabhakaran, A. Kulkarni, G.Vasanth, S. Kalainathan, P. Shukla, and V.K. Vasudevan. (2018) Laser shock peening without coating induced residual stress distribution, wettability characteristics and enhanced pitting corrosion of austenitic stainless steel, Applied Surface Science 428C, 17-30.